Where has Kim Jong-un been?

(Reuters) - Young North Korean leader Kim Jong Un is suffering from "discomfort", state media has said in the first official acknowledgement of ill health after a prolonged period out of the public eye.

Kim, 31, who is frequently the centerpiece of the isolated country's propaganda, has not been photographed by state media since appearing at a concert alongside his wife on Sept. 3, fueling speculation he is suffering from bad health.

He had been seen walking with a limp since an event with key officials in July and in a pre-recorded documentary broadcast by state media on Thursday appeared to have difficulty walking.

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Where has Kim Jong-un been?

In this image taken from video North Korean leader Kim Jong Un, center, salutes during a military parade marking the 65th anniversary of the country's founding, Monday, Sept. 9, 2013, in Pyongyang, North Korea. (AP Photo/KRT via AP Video)

In this image taken from video North Korean leader Kim Jong Un, center, salutes during a military parade marking the 65th anniversary of the country's founding, Monday, Sept. 9, 2013, in Pyongyang, North Korea. (AP Photo/KRT via AP Video) TV OUT, NORTH KOREA OUT

FILE - In this July 27, 2013 file photo, North Korea's leader Kim Jong Un waves to spectators and participants of a mass military parade celebrating the 60th anniversary of the Korean War armistice in Pyongyang, North Korea. North Korea's young leader wasn't in his customary seat as the country convened its rubber-stamp parliament Thursday, Sept. 25, 2014, adding to South Korean media speculation that Kim may be ill. (AP Photo/Wong Maye-E, File)

ADDS WHERE KIM APPEARED - A man watches a TV news program at the Seoul Railway Station in Seoul, South Korea, Tuesday, Oct. 14, 2014, showing North Korean leader Kim Jong Un using a cane, reportedly during his first public appearance in five weeks in Pyongyang, North Korea. Kim has made his first public appearance in five weeks, smiling broadly and supporting himself with a cane while touring the newly built Wisong Scientists Residential District and another new institute in Pyongyang, state media reported Tuesday, ending an absence that drove a frenzy of global speculation that something was amiss with the country's most powerful person. (AP Photo/Lee Jin-man)

ADDS WHERE KIM APPEARED - A shopper passes by TV monitors displaying a news program at an electronic shop in Seoul, South Korea, Tuesday, Oct. 14, 2014, showing a photo of North Korean leader Kim Jong Un smiling, reportedly during his first public appearance in five weeks in Pyongyang, North Korea. Kim has made his first public appearance in five weeks, smiling broadly and supporting himself with a cane while touring the newly built Wisong Scientists Residential District and another new institute in Pyongyang, state media reported Tuesday, ending an absence that drove a frenzy of global speculation that something was amiss with the country's most powerful person. (AP Photo/Ahn Young-joon)

A photo of North Korean leader Kim Jong Un walking with a stick in Pyongyang, North Korea, is carried on the front page of a South Korea's English newspaper kept at a newspaper distributing station in Seoul, South Korea, Tuesday evening, Oct. 14, 2014. Kim, smiling broadly and supporting himself with a walking stick, appeared earlier Tuesday in the North's state media for the first time in nearly six weeks, ending rumors that he was gravely ill, deposed or worse. (AP Photo/Ahn Young-joon)

In this image taken from video, North Korean leader Kim Jong Un attends an event to mark the second anniversary of the death of his father, former leader Kim Jong Il, in Pyongyang, North Korea Tuesday, Dec. 17, 2013. (AP Photo/KRT via AP Video)

FILE - In this Thursday, July 25, 2013 file photo, North Korean leader Kim Jong Un arrives at the cemeteries of fallen fighters of the Korean People's Army (KPA) in Pyongyang, as part of ceremonies marking the 60th anniversary of the signing of the armistice that ended hostilities on the Korean peninsula. North Korea's propaganda machine has long kept alive the myth of a serene, all-powerful ruling dynasty that enjoyed universal love and support at home. In a single stroke last week, that came crashing down. In attempting to justify the execution of his uncle, who was also considered the North's No. 2 official, young leader Kim Jong Un has given the world a rare look behind the scenes of a notoriously hard-to-read government. (AP Photo/Wong Maye-E, File)

In this Saturday, July 27, 2013 photo, North Korean leader Kim Jong Un waves to war veterans during a mass military parade celebrating the 60th anniversary of the Korean War armistice in Pyongyang, North Korea. A Malaysian university faced public criticism Thursday for awarding an honorary doctorate in economics to North Korean leader Kim Jong Un, whose country is among the poorest in the world. (AP Photo/Wong Maye-E)

North Korean leader Kim Jong Un, right, arrives at the cemeteries of fallen fighters of the Korean People's Army (KPA) on Thursday, July 25, 2013 in Pyongyang, North Korea as part of ceremonies marking the 60th anniversary of the signing of the armistice that ended hostilities on the Korean peninsula. (AP Photo/Wong Maye-E)

Portraits of the late North Korean leaders Kim Il Sung and Kim Jong Il are seen displayed as North Koreans participate in the "Arirang" mass games on Monday, July 22, 2013 in pyongyang, North Korea. North Korea has revealed a new rendition of the "Arirang" mass games, the song-and-dance ensemble. This yearâs performance was timed to debut for the 60th anniversary of the end of the Korean War, and features new scenes focusing on leader Kim Jong Unâs directives. (AP Photo/Wong Maye-E)

In this Feb. 16, 2013 image made from video, North Korean leader Kim Jong Un, left, along with his aunt Kim Kyong Hui, right, attends a statue unveiling ceremony in Pyongyang, North Korea on the anniversary of late North Korean leader Kim Jong Il's birthday. The aunt of North Korean leader Kim Jong Un has been named to an ad-hoc state committee, the country's official media reported Sunday, Dec. 15, 2013, an indication that the execution of her husband and the country's No. 2, Jang Song Thaek ,has not immediately diminished her influence. (AP Photo/KRT via AP Video, File) TV OUT, NORTH KOREA OUT

In this Feb. 16, 2013 image made from video, North Korean leader Kim Jong Un, center, waves as he attends a statue unveiling ceremony at Mangyongdae Revolutionary School in Pyongyang, North Korea on the anniversary of late North Korean leader Kim Jong Il's birthday. (AP Photo/KRT via AP Video) TV OUT, NORTH KOREA OUT

In this image taken from video made available on Wednesday, Jan. 1, 2014, North Korean leader Kim Jong Un delivers an annual New Year's Day message in Pyongyang, North Korea. Kim boasted Wednesday that North Korea enters the new year on a surge of strength because of the elimination of "factionalist filth" - a reference to the young leader's once powerful uncle, whose execution last month raised questions about Kim's grip on power. (AP Photo/KRT via AP Video) TV OUT, NORTH KOREA OUT

In this Jan. 28, 2013 image made from video, North Korean leader Kim Jong Un delivers opening remarks at the Fourth Meeting of Secretaries of Cells of the Workers' Party of Korea, in Pyongyang, North Korea. Kim convened top security and foreign affairs officials and ordered them to take "substantial and high-profile important state measures," state media said Sunday, fueling speculation that he plans to push forward with a threat to explode a nuclear device in defiance of the United Nations. (AP Photo/KRT via AP Video) NORTH KOREA OUT, TV OUT

In this Friday, Dec. 21, 2012 image made from video, North Korean leader Kim Jong Un speaks at a banquet for rocket scientists in Pyongyang, North Korea. Kim has called for the development of more powerful rockets after last week's successful launch of a satellite into space. (AP Photo/KRT via AP Video) NORTH KOREA OUT

South Korean protesters hold the pictures of North Korean leader Kim Jong Un during a rally denouncing North Korea's rocket launch in Seoul, South Korea, Wednesday, Dec. 12, 2012. North Korea successfully fired a long-range rocket on Wednesday, defying international warnings as the regime of Kim Jong Un took a giant step forward in its quest to develop the technology to deliver a nuclear warhead. The letters read "Out, Pro-North Korea politic." (AP Photo/Lee Jin-man)

A cutout of North Korean leader Kim Jong Un is displayed during a protest denouncing North Korea for trying to intervene in the upcoming South Korean presidential election scheduled for Dec. 20, in Seoul, South Korea, Friday, Oct. 12, 2012. The cutout reads "Novice." (AP Photo/Ahn Young-joon)

In this video image taken from KRT, North Korean leader Kim Jong Un holds up his credential at the Supreme People's Assembly's second meeting of the year, in Pyongyang, North Korea, Tuesday, Sept. 25, 2012. North Korea's parliament convened Tuesday for the second time in six months, passing a law that adds one year of compulsory education for children in the socialist nation, the first publicly-announced policy change under leader Kim. (AP Photo/KRT via AP video) NORTH KOREA OUT

In this Wednesday, July 25, 2012 photo released by the Korean Central News Agency (KCNA) and distributed in Tokyo by the Korea News Service Thursday, July 26, 2012, North Korean leader Kim Jong Un, center, accompanied by his wife Ri Sol Ju, right, waves to the crowd as they inspect the Rungna People's Pleasure Ground in Pyongyang. (AP Photo/Korean Central News Agency via Korea News Service) JAPAN OUT UNTIL 14 DAYS AFTER THE DAY OF TRANSMISSION

In this image released by by the Korean Central News Agency (KCNA) and distributed in Tokyo by the Korea News Service on Wednesday July 25, 2012 North Korean leader Kim Jong-Un, centre, Ri Sol Ju, centre left. visit the Rungna People's Pleasure Ground, which is nearing completion, in this undated picture North Korea's new, young leader Kim Jong Un is married, state TV reported Wednesday for the first time in a brief and otherwise routine announcement that ends weeks of speculation about a beautiful woman who has accompanied him to recent public events. Kim toured an amusement park with his "wife, comrade Ri Sol Ju" on Tuesday, while a crowd cheered for the leader, the news anchor said without giving any more details about Ri, including how long they had been married. (AP Photo/KCNA KNS) JAPAN OUT UNTIL 14 DAYS AFTER THE DAY OF TRANSMISSION

North Korea's new commander in chief, Kim Jong Un is displayed on a giant screen during a concert on the eve of the 80th anniversary of the founding of the North Korean army in Pyongyang, North Korea, Tuesday, April 24, 2012. (AP Photo/Ng Han Guan)

An effigy of North Korean leader Kim Jong Un is burned by anti-North Korea protesters during a rally denouncing the North's recent announcement in Seoul, South Korea, Tuesday, April 24, 2012. North Korea sharply escalated the rhetoric against its southern rival, claiming it will soon conduct "special actions" that would reduce South Korea's conservative government to ashes within minutes. (AP Photo/Lee Jin-man)

North Korean leader Kim Jong Un waves from a balcony at the end of a mass military parade in Pyongyang's Kim Il Sung Square to celebrate 100 years since the birth of his grandfather, and North Korean founder, Kim Il Sung on Sunday, April 15, 2012. Kim delivered his first public televised speech Sunday, just two days after a failed rocket launch, portraying himself as a strong military chief unafraid of foreign powers during festivities meant to glorify his grandfather, North Korea founder Kim Il Sung. (AP Photo/Ng Han Guan)

In this April 13, 2012 image made Saturday, April 14, 2012, from KRT video, North Korean leader Kim Jong Un claps hands during the meeting of the Supreme People's Assembly in Pyongyang, North Korea. North Korean leader Kim Jong Un has been installed as the new head of the powerful National Defence Commission in the meeting Friday. (AP Photo/KRT via AP video) NORTH KOREA OUT, TV OUT

In this undated photo released by the Korean Central News Agency and distributed in Tokyo by the Korea News Service on Monday, Jan. 23, 2012, North Korean leader Kim Jong Un accompanied by Korean People's Army soldiers visits a KPA unit at an undisclosed location in North Korea. (AP Photo/Korean Central News Agency via Korea News Service) JAPAN OUT UNTIL 14 DAYS AFTER THE DAY OF TRANSMISSION

In this undated photo released by the Korean Central News Agency and distributed in Tokyo by the Korea News Service Saturday, Jan. 21, 2012, North Korean leader Kim Jong Un waves during his visit to the Korean People's Army (KPA) Unit 3870 at an undisclosed location in North Korea. (AP Photo/Korean Central News Agency via Korea News Service) JAPAN OUT UNTIL 14 DAYS AFTER THE DAY OF TRANSMISSION

In this image made from KRT television, Kim Jong Un, North Korean leader Kim Jong Il's youngest known son and successor, wipes his eyes with handkerchief as he views his father's body displayed in a glass coffin, not in photo, at Kumsusan Memorial Palace in Pyongyang, North Korea Friday, Dec. 23, 2011. Kim Jong Un, hailed as the "great successor" in state media, visited his father's coffin again Friday. (AP Photo/KRT via APTN) TV OUT, NORTH KOREA OUT

An effigy of North Korean leader Kim Jong Un is displayed during a rally to mark the the third anniversary of North Koreaâs artillery attack on the Yeonpyeong island, in Seoul, South Korea, Saturday, Nov. 23, 2013. Four people, including two marines and two civilians, were killed by North Korea's attack. The banner reads "Hang Kim Jong Un, Strike Pyongyang and Get rid of pro-North ." (AP Photo/Ahn Young-joon)

SEOUL, SOUTH KOREA - DECEMBER 17: South Korean conservative protesters burn an effigy of North Korean leader Kim Jong-Un during an anti-North Korea protest marking the second anniversary of former North Korean leader Kim Jong Il's death on December 17, 2013 in Seoul, South Korea. The tension is heightened in South Korea since the report that North Korea has executed Jang Song-Thaek, Kim Jong Un's uncle on December 13, 2013. On December 17, 2013 North Korea also commemorates two years since the death of former leader Kim Jong-il. (Photo by Chung Sung-Jun/Getty Images)

SEOUL, SOUTH KOREA - DECEMBER 17: South Korean conservative protesters shout slogans during an anti-North Korea protest marking the second anniversary of former North Korean leader Kim Jong Il's death on December 17, 2013 in Seoul, South Korea. The tension is heightened in South Korea since the report that North Korea has executed Jang Song-Thaek, Kim Jong Un's uncle on December 13, 2013. On December 17, 2013 North Korea also commemorates two years since the death of former leader Kim Jong-il. (Photo by Chung Sung-Jun/Getty Images)

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"The wealth and prosperity of our socialism is thanks to the painstaking efforts of our marshal, who keeps lighting the path for the people, like the flicker of a flame, despite suffering discomfort," a voice over for the hour-long documentary said.

The documentary was followed by a pre-recorded broadcast of a North Korean Supreme People's Assembly meeting from which Kim Jong Un was notably absent.

Kim has rapidly gained weight since coming to power after his father died of a heart attack in 2011, photos released by state media show.

North Korea observers speculate Kim's weight and family background may have contributed to his condition.

"Based on his gait, it appears he has gout - something (due to) diet and genetic predisposition that has affected other members of the Kim family," said Michael Madden, an expert on the North Korean leadership and contributor to the 38 North website.